The neurovascular unit and combination treatment strategies for stroke

Stroke-induced blood-brain barrier breakdown along the vascular tree - No preferential affection of arteries in different animal models and in humans

Stroke-induced blood-brain barrier breakdown promotes complications like cerebral edema and hemorrhagic transformation, especially in association with therapeutical recanalization of occluded vessels. As arteries, capillaries and veins display distinct functional and morphological characteristics, we here investigated patterns of blood-brain barrier breakdown for each segment of the vascular tree in rodent models of embolic, permanent, and transient middle cerebral artery occlusion, added by analyses of human stroke tissue. Twenty-four hours after ischemia induction, loss of blood-brain barrier function towards FITC-albumin was equally observed for arteries, capillaries, and veins in rodent brains. Noteworthy, veins showed highest ratios of leaky vessels, whereas capillaries exhibited the most and arteries the least widespread perivascular tracer extravasation. In contrast, human autoptic stroke tissue exhibited pronounced extravasations of albumin around arteries and veins, while the pericapillary immunoreactivity appeared only faint. Although electron microscopy revealed comparable alterations of the arterial and capillary endothelium throughout the applied animal models, structural loss of arterial smooth muscle cells was only observed in the translationally relevant model of embolic middle cerebral artery occlusion. In light of the so far available concepts of stroke treatment, the consideration of a differential vascular pathophysiology along the cerebral vasculature is likely to allow development of novel effective treatment strategies.

Delayed histochemical alterations within the neurovascular unit due to transient focal cerebral ischemia and experimental treatment with neurotrophic factors

Current stroke therapy is focused on recanalizing strategies, but neuroprotective co-treatments are still lacking. Modern concepts of the ischemia-affected neurovascular unit (NVU) and surrounding penumbra emphasize the complexity during the transition from initial damaging to regenerative processes. While early treatment with neurotrophic factors was shown to result in lesion size reduction and blood-brain barrier (BBB) stabilization, cellular consequences from these treatments are poorly understood. This study explored delayed cellular responses not only to ischemic stroke, but also to an early treatment with neurotrophic factors. Rats underwent 60 minutes of focal cerebral ischemia. Fluorescence labeling was applied to sections from brains perfused 7 days after ischemia. Analyses focused on NVU constituents including the vasculature, astrocytes and microglia in the ischemic striatum, the border zone and the contralateral hemisphere. In addition to histochemical signs of BBB breakdown, a strong up-regulation of collagen IV and microglia activation occurred within the ischemic core with simultaneous degradation of astrocytes and their endfeet. Activated astroglia were mainly depicted at the border zone in terms of a glial scar formation. Early treatment with pigment epithelium-derived factor (PEDF) resulted in an attenuation of the usually up-regulated collagen IV-immunoreactivity. However, glial activation was not influenced by treatment with PEDF or the epidermal growth factor (EGF). In conclusion, these data on ischemia-induced cellular reactions within the NVU might help to develop treatments addressing the transition from injury towards regeneration. Thereby, the integrity of the vasculature in close relation to neighboring structures like astrocytes appears as a promising target.

PARK2-dependent mitophagy induced by acidic postconditioning protects against focal cerebral ischemia and extends the reperfusion window

Prompt reperfusion after cerebral ischemia is critical for neuronal survival. Any strategies that extend the limited reperfusion window will be of great importance. Acidic postconditioning (APC) is a mild acidosis treatment that involves inhaling CO₂ during reperfusion following ischemia. APC attenuates ischemic brain injury although the underlying mechanisms have not been elucidated. Here we report that APC reinforces ischemia-reperfusion-induced mitophagy in middle cortical artery occlusion (MCAO)-treated mice, and in oxygen-glucose deprivation (OGD)-treated brain slices and neurons. Inhibition of mitophagy compromises neuroprotection conferred by APC. Furthermore, mitophagy and neuroprotection are abolished in Park2 knockout mice, indicating that APC-induced mitophagy is facilitated by the recruitment of PARK2 to mitochondria. Importantly, in MCAO mice, APC treatment extended the effective reperfusion window from 2 to 4 h, and this window was further extended to 6 h by exogenously expressing PARK2. Taken together, we found that PARK2-dependent APC-induced mitophagy renders the brain resistant to ischemic injury. APC treatment could be a favorable strategy to extend the thrombolytic time window for stroke therapy.

One-Compound-Multi-Target: Combination Prospect of Natural Compounds with Thrombolytic Therapy in Acute Ischemic Stroke

Tissue plasminogen activator (t-PA) is the only FDA-approved drug for acute ischemic stroke treatment, but its clinical use is limited due to the narrow therapeutic time window and severe adverse effects, including hemorrhagic transformation (HT) and neurotoxicity. One of the potential resolutions is to use adjunct therapies to reduce the side effects and extend t-PA's therapeutic time window. However, therapies modulating single target seem not to be satisfied, and a multitarget strategy is warranted to resolve such complex disease. Recently, large amount of efforts have been made to explore the active compounds from herbal supplements to treat ischemic stroke. Some natural compounds revealed both neuro- and bloodbrain- barrier (BBB)-protective effects by concurrently targeting multiple cellular signaling pathways in cerebral ischemia-reperfusion injury. Thus, those compounds are potential to be one-drug-multi-target agents as combined therapy with t-PA for ischemic stroke. In this review article, we summarize current progress about molecular targets involving in t-PA-mediated HT and neurotoxicity in ischemic brain injury. Based on these targets, we select 23 promising compounds from currently available literature with the bioactivities simultaneously targeting several important molecular targets. We propose that those compounds merit further investigation as combined therapy with t-PA. Finally, we discuss the potential drawbacks of the natural compounds' studies and raise several important issues to be addressed in the future for the development of natural compound as an adjunct therapy.

A Prospective Safety Trial of Atorvastatin Treatment to Assess Rebleeding after Spontaneous Intracerebral Hemorrhage: A Serial MRI Investigation

AIM

This study was designed to determine any rebleeding after atorvastatin treatment following spontaneous intracerebral hemorrhage (ICH) in a prospective safety trial.

PATIENTS

Atorvastatin (80 mg/day) therapy was initiated in 6 patients with primary ICH with admission Glasgow Coma Score (GCS) >5 within 24 hours of ictus and continued for 7 days, with the dose tapered and treatment terminated over the next 5 days. Patients were studied longitudinally by multiparametric magnetic resonance imaging (MRI) at three time points: acute (3 to 5 days), subacute (4 to 6 weeks) and chronic (3 to 4 months). Imaging sequences included T₁, T₂-weighted imaging (T₂WI), diffusion tensor imaging (DTI) and contrast-enhanced MRI measures of cerebral perfusion, blood volume and blood-brain barrier (BBB) permeability. Susceptibility weighted imaging (SWI) was used to identify primary ICH and to check for secondary rebleeding. Final outcome was assessed using Glasgow Outcome Score (GOS) at 3-4 months.

RESULTS

Mean admission GCS was 13.2±4.0 and mean GOS at 3 months was 4.5±0.6. Hemorrhagic lesions were segmented into core and rim areas. Mean lesion volumes decreased significantly between the acute and chronic study time points (p=0.008). Average ipsilateral hemispheric tissue loss at 3 to 4 months was 11.4±4.6 cm³. MRI showed acutely reduced CBF (p=0.004) and CBV (p=0.002) in the rim, followed by steady normalization. Apparent diffusion coefficient of water (ADC) in the rim demonstrated no alterations at any of the time points (p>0.2). The T₂ values were significantly elevated in the rim acutely (p=0.02), but later returned to baseline. The ICH core showed sustained low CBF and CBV values concurrent with a small reduction in ADC acutely, but significant ADC elevation at the end suggestive of irreversible injury.

CONCLUSION

Despite the presence of a small, probably permanent, cerebral lesion in the ICH core, no patients exhibited post-treatment rebleeding. These data suggest that larger, Phase 2 trials are warranted to establish long term clinical safety of atorvastatin in spontaneous ICH.

Neuroprotective effects of Aceglutamide on motor function in a rat model of cerebral ischemia and reperfusion

PURPOSE

To investigate the effect and underlying mechanism of Aceglutamide on motor dysfunction in rats after cerebral ischemia-reperfusion.

METHODS

Adult male Sprague-Dawley rats were subjected to 2 h transient middle cerebral artery occlusion (MCAO). Aceglutamide or vehicle was intraperitoneally given to rats at 24 h after reperfusion and lasted for 14 days. Subsequently functional recovery was assessed and number of tyrosine hydroxylase (TH)-positive neurons in substantia nigra (SN) was analyzed. Tumor necrosis factor receptor-associated factor 1(TRAF1), P-Akt and Bcl-2/Bax were determined in mesencephalic tissue by Western blot method. PC12 cells and primary cultured mesencephalic neurons were employed to further investigate the mechanism of Aceglutamide.

RESULTS

Aceglutamide treatment improved behavioral functions, reduced the infarction volume, and elevated the number of TH-positive neurons in the SN. Moreover, Aceglutamide significantly attenuated neuronal apoptosis in the SN. Meanwhile Aceglutamide treatment significantly inhibited the expression of TRAF1 and up-regulated the expression of P-Akt and Bcl-2/Bax ratio both in vitro and in vivo.

CONCLUSIONS

Aceglutamide ameliorated motor dysfunction and delayed neuronal death in the SN after ischemia, which involved the inhibition of pro-apoptotic factor TRAF1 and activation of Akt/Bcl-2 signaling pathway. These data provided experimental information for applying Aceglutamide to ischemic stroke treatment.

Effects of Xiaoshuan enteric-coated capsule on neurovascular functions assessed by quantitative multiparametric MRI in a rat model of permanent cerebral ischemia

Background

Buyang Huanwu Decoction (BYHWD) is a Traditional Chinese Medicine (TCM) formula for treating stroke-induced disability. Xiaoshuan enteric-coated capsule (XSECC), derived from the formula BYHWD, is a drug approved by the China Food and Drug Administration (CFDA) for stroke management. To further investigate the potential protective effects of XSECC on neurovascular functions, we endeavour to monitor the neurovascular functions using multimodal magnetic resonance imaging (MRI) and evaluated histopathological changes of neurovascular unit (NVU) after stroke.

Methods

Ischemic stroke was induced by permanent middle cerebral artery occlusion (pMCAO). XSECC (420 mg/kg) was orally administered 2 h after stroke and daily thereafter. T2-weighted imaging (T2WI), T2 relaxometry mapping and diffusion tensor imaging (DTI) were used to measure cerebral infarct volume, edema and white matter fiber integrity, respectively. Neurochemical metabolite levels were monitored by ¹H-magnetic resonance spectroscopy (¹H-MRS). Arterial spin labeling (ASL) – cerebral blood flow (CBF) measurements and structural magnetic resonance angiography (MRA) images provided real-time and dynamic information about vascular hemodynamic dysfunction on the 3rd, 7th and 14th days after pMCAO. At the last imaging time point, immunohistochemistry, immunofluorescence as well as transmission electron microscopy (TEM) were used to test the microscopic and ultrastructural changes of NVU.

Results

T2WI, T2 relaxometry mapping and Fractional anisotropy (FA) in DTI showed that XSECC significantly reduced cerebral infarct volume, relieved edema and alleviated nerve fiber injuries, respectively. ¹H-MRS provided information about improvement of neuronal/glial metabolism after XSECC treatment. Moreover, ASL – CBF measurements combined with MRA showed that XSECC significantly increased CBF and vascular signal strength and alleviated ischemia-induced morphological changes of arteries in ischemic hemisphere within 14 days after stroke. In addition, neuron specific nuclear protein (NeuN), glial fibrillary acidic protein (GFAP), CD34 staining and TEM detection indicated that XSECC not only ameliorated neuronal injury, but also reduced endothelial damage and inhibited astrocyte proliferation.

Conclusions

Our results suggested that XSECC has multi-target neurovascular protective effects on ischemic stroke, which may be closely correlated with the improvement of cerebral blood supply and neuronal/glial metabolism.

Normobaric Hyperoxia Extends Neuro- and Vaso-Protection of N-Acetylcysteine in Transient Focal Ischemia

N-acetylcysteine (NAC), a precursor of glutathione that reduces reperfusion-induced injury, has been shown protection when it was administered pre-ischemia. However, less is known about the effect when it was given post-ischemia and there is no positive result associated with anti-oxidant in clinical trials. This study investigated the neuro- and vaso-protection of post-ischemia NAC administration as well as combining NAC with normobaric hyperoxia (NBO). Male Sprague-Dawley rats were exposed to NBO or normoxia during 2-h occlusion of the middle cerebral artery, followed by 48-h reperfusion. NAC or vehicle was intraperitoneally administered to rats immediately before reperfusion onset. NAC and NBO treatments produced 1.2 and 30 % reduction of infarction volume, respectively, and combination treatment showed greater reduction (59.8 %) as well as more decrease of hemispheric swelling volume. Of note, combination therapy showed improved neurological assessment and motor function which were sustained for 7 days after reperfusion. We also determined that the combination therapy showed greater inhibitory effects on tight junction protein degradation accompanied by Evan's blue extravasation, hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) induction, and poly ADP-ribose polymerase (PARP)-1 activation in ischemic brain tissue. Our results showed that although post-ischemia NAC administration had limited protection, combination treatment of NAC plus NBO effectively prevented blood-brain barrier (BBB) damage and significantly improved the outcome of brain injury, providing new evidence to support the concept that "cocktail" treatment targeting different stages provides better neuro- and vaso-protection than current individual treatment that has all failed in their clinical trials.

Cocktail treatment, a promising strategy to treat acute cerebral ischemic stroke?

Up to now, over 1,000 experimental treatments found in cells and rodents have been difficult to translate to human ischemic stroke. Since ischemia and reperfusion, two separate stages of ischemic stroke, have different pathophysiological mechanisms leading to brain injury, a combination of protective agents targeting ischemia and reperfusion respectively may obtain substantially better results than a single agent. Normobaric hyperoxia (NBO) has been shown to exhibit neuro- and vaso-protective effects by improving tissue oxygenation when it is given during ischemia, however the effect of NBO would diminish when the duration of ischemia and reperfusion was extended. Therefore, during reperfusion drug treatment targeting inflammation, oxidative stress and free radical scavenger would be a useful adjuvant to extend the therapeutic window of tissue plasminogen activator, the only United States Food and Drug Administration (FDA) approved treatment for acute ischemic stroke. In this review, we discussed the neuro- and vaso-protective effects of NBO and recent finding of combining NBO with other drugs.

Pharmacokinetics of 21 active components in focal cerebral ischemic rats after oral administration of the active fraction of Xiao-Xu-Ming decoction

The Xiao-Xu-Ming decoction (XXMD) is a traditional Chinese medicine prescription that is clinically used for the treatment of stroke. The active fraction of XXMD (AF-XXMD) exhibits pharmacological effects that are similar to those of XXMD. In this study, 21 primary compounds of AF-XXMD with potential anti-ischemic-stroke activities were selected as effective candidates to perform comparisons of their pharmacokinetic differences between control and cerebral ischemic rats and to characterize their pharmacokinetic behaviors in cerebral ischemic rats. After oral administration of AF-XXMD to control and cerebral ischemic rats, plasma and brain were harvested and analyzed using liquid chromatography coupled with tandem mass spectrometry. Reverse molecular docking results indicate that 21 AF-XXMD-derived compounds exert potential neuroprotection, anti- inflammation, and vascular dilation effects via interaction with multiple targets in stroke-related pathways. The blood-brain permeability, cerebral exposure and brain region distribution of these compounds were found to change in cerebral ischemic models. Flavonoids were identified as the predominant form in plasma, whereas chromones were found to be the major form in the brain, and alkaloids possessed moderate blood-brain permeability. Collectively, the cerebral pharmacokinetic behaviors of chromones, flavonoids and alkaloids were found to change under pathological conditions. The efficacy of AF-XXMD against cerebral ischemia is relevant to the synergistic effects of these compounds in targeting different receptors and pathways. Chromones exhibit relatively high brain permeability, and their activity and mechanism warrant further investigation.

YiQiFuMai powder injection ameliorates blood-brain barrier dysfunction and brain edema after focal cerebral ischemia-reperfusion injury in mice

YiQiFuMai powder injection (YQFM) is a modern preparation derived from the traditional Chinese medicine Sheng-Mai-San. YQFM is widely used in clinical practice in the People’s Republic of China, mainly for the treatment of microcirculatory disturbance-related diseases. However, little is known about its role in animals with ischemic stroke. The aim of this study was to examine the effect of YQFM on brain edema and blood–brain barrier (BBB) dysfunction induced by cerebral ischemia–reperfusion (I/R) injury. Male C57BL/6J mice underwent right middle cerebral artery occlusion for 1 hour with a subsequent 24-hour reperfusion to produce I/R injury. YQFM (three doses: 0.336, 0.671, and 1.342 g/kg) was then given intraperitoneally (IP). The results demonstrated that YQFM significantly decreased infarct size, improved neurological deficits, reduced brain water content, and increased cerebral blood flow after I/R injury. 18F-fluorodeoxyglucose micro-positron emission tomography imaging and hematoxylin and eosin staining results indicated that YQFM is able to ameliorate brain metabolism and histopathological damage after I/R. Moreover, YQFM administration reduced BBB leakage and upregulated the expression of zona occludens-1 (ZO-1) and occludin, which was confirmed by Evans Blue extravasation, Western blotting, and immunofluorescence assay. Our findings suggest that YQFM provides protection against focal cerebral I/R injury in mice, possibly by improving BBB dysfunction via upregulation of the expression of tight junction proteins.

The Role of Activated Microglia and Resident Macrophages in the Neurovascular Unit during Cerebral Ischemia: Is the Jury Still Out?

Paracrine signaling in the neurovascular unit (NVU) is aimed to adjust the supply of oxygen and nutrients to metabolic demands of the brain in a feed-forward manner. Cerebral ischemia (CI) severely disrupts this homeostatic mechanism and also causes activation of microglia and resident macrophages in the brain. Contradictory data exist on the time pattern of microglial activation and polarization during CI, on molecular mechanisms that trigger them and on effects of microglia-derived cytokines on brain cells. It appears that conditions that occur during transient ischemia or in the penumbra of focal ischemia in vivo or equivalent conditions in vitro trigger polarization of resting microglia/macrophages into the M2 phenotype, which mainly exerts anti-inflammatory and protective effects in the brain, while prolonged ischemia with abundant necrosis promotes microglial polarization into the M1 phenotype. During the later stages of recovery, microglia that polarized initially into the M2 phenotype can shift into the M1 phenotype. Thus, it appears that cells with both phenotypes are present in the affected area, but their relative amount changes in time and probably depends on the proximity to the ischemic core. It was assumed that cells with the M1 phenotype exert detrimental effects on neurons and contribute to the blood-brain barrier opening. Several M1 phenotype-specific cytokines exert protective effects on astrocytes, which could be important for reactive gliosis occurring after ischemia. Thus, whether or not suppression of microglial activity after CI is beneficial for neurological outcome still remains unclear and current evidence suggests that no simple answer could be given to this question.

Opening the window: Ischemic postconditioning reduces the hyperemic response of delayed tissue plasminogen activator and extends its therapeutic time window in an embolic stroke model

It has been reported that ischemic postconditioning (PC) changes the reperfusion pattern in permanent or transient models of stroke and confers neuroprotection. However, the effects of PC and subsequent use of tissue plasminogen activator (tPA) for the treatment of embolic stroke have not yet been investigated. Rats were subjected to stroke by injection of a preformed clot into the middle cerebral artery and randomly assigned to vehicle (saline 0.1 ml/100 g), tPA (3 mg/kg), PC only or PC+tPA (3 mg/kg). tPA was injected at 6 h after embolic stroke and PC was conducted at 6.5 h after ischemia by using five cycles of a 10 s occlusion and 30 s of reopening of the bilateral common carotid arteries. Cerebral blood flow (CBF) was monitored for 60 min from the time of tPA injection. Infarct size, blood brain barrier disruption, edema, neurological deficits, reactive oxygen species and apoptosis were measured 2 days later. PC decreased infarct volume, but PC+tPA was more neuroprotective than PC alone. While tPA alone dramatically increased CBF, conducting PC caused a gradual increase in CBF. A combination of PC+tPA reduced BBB leakage, brain edema, apoptosis and reactive oxygen species levels. Furthermore, a combination of PC+tPA improved neurological functions at 48 h after the induced stroke. In conclusion, PC hampered malignant hyperemia after reperfusion with tPA and extended its therapeutic window up to 6 h. Compared to PC alone, combination of thrombolysis and PC showed a better neuroprotection.

Pharmacokinetics, biodistribution and metabolism of squalenoyl adenosine nanoparticles in mice using dual radio-labeling and radio-HPLC analysis

Adenosine is a pleiotropic endogenous nucleoside with potential neuroprotective pharmacological activity. However, clinical use of adenosine is hampered by its extremely fast metabolization. To overcome this limitation, we recently developed a new squalenoyl nanomedicine of adenosine [Squalenoyl-Adenosine (SQAd)] by covalent linkage of this nucleoside to the squalene, a natural lipid. The resulting nanoassemblies (NAs) displayed a dramatic pharmacological activity both in cerebral ischemia and spinal cord injury pre-clinical models. The aim of the present study was to investigate the plasma profile and tissue distribution of SQAd NAs using both Squalenoyl-[³H]-Adenosine NAs and [¹⁴C]-Squalenoyl-Adenosine NAs as respective tracers of adenosine and squalene moieties of the SQAd bioconjugate. This study was completed by radio-HPLC analysis allowing to determine the metabolization profile of SQAd. We report here that SQAd NAs allowed a sustained circulation of adenosine under its prodrug form (SQAd) for at least 1 h after intravenous administration, when free adenosine was metabolized within seconds after injection. Moreover, the squalenoylation of adenosine and its formulation as NAs also significantly modified biodistribution, as SQAd NAs were mainly captured by the liver and spleen, allowing a significant release of adenosine in the liver parenchyma. Altogether, these results suggest that SQAd NAs provided a reservoir of adenosine into the bloodstream which may explain the previously observed neuroprotective efficacy of SQAd NAs against cerebral ischemia and spinal cord injury.

Focal embolic cerebral ischemia in the rat

Animal models of focal cerebral ischemia are well accepted for investigating the pathogenesis and potential treatment strategies for human stroke. Occlusion of the middle cerebral artery (MCA) with an endovascular filament is a widely used model to induce focal cerebral ischemia. However, this model is not amenable to thrombolytic therapies. As thrombolysis with recombinant tissue plasminogen activator (rtPA) is a standard of care within 4.5 h of human stroke onset, suitable animal models that mimic cellular and molecular mechanisms of thrombosis and thrombolysis of stroke are required. By occluding the MCA with a fibrin-rich allogeneic clot, we previously developed an embolic model of MCA occlusion in the rat, which recapitulates the key components of thrombotic development and of thrombolytic therapy of rtPA observed from human ischemic stroke. Here we describe in detail the surgical procedures of our model, including preparing emboli from rat donors. These procedures can be typically completed within ∼30 min, and they are highly adaptable to other strains of rats, as well as mice, in both sexes. Thus, this model provides a powerful tool for translational stroke research.

In Vivo Imaging of the Mouse Neurovascular Unit Under Chronic Cerebral Hypoperfusion

Background and Purpose—

Proper brain function is maintained by an integrated system called the neurovascular unit (NVU) comprised cellular and acellular elements. Although the individual features of specific neurovascular components are understood, it is unknown how they respond to ischemic stress as a functional unit. Therefore, we established an in vivo imaging method and clarified the NVU response to chronic cerebral hypoperfusion.

Methods—

Green mice (b-act-EGFP) with SR101 plasma labeling were used in this experiment. A closed cranial window was made over the left somatosensory cortex. To mimic chronic cerebral hypoperfusion, mice were subjected to bilateral common carotid artery stenosis operations using microcoils. In vivo real-time imaging was performed using 2-photon laser-scanning microscopy during the preoperative period, and after 1 day and 1 and 2 weeks of bilateral common carotid artery stenosis or sham operations.

Results—

Our method allowed 3-dimensional observation of most of the components of the NVU, as well as dynamic capillary microcirculation. Under chronic cerebral hypoperfusion, we did not detect any structural changes of each cellular component in the NVU; however, impairment of microcirculation was detected over a prolonged period. In the pial small arteries and veins, rolling and adhesion of leukocyte were detected, more prominently in the latter. In the deep cortical capillaries, flow stagnation because of leukocyte plugging was frequently observed.

Conclusions—

We established an in vivo imaging method for real-time visualization of the NVU. It seems that under chronic cerebral hypoperfusion, leukocyte activation has a critical role in microcirculation disturbance.

Erythropoietin increases bioavailability of tetrahydrobiopterin and protects cerebral microvasculature against oxidative stress induced by eNOS uncoupling

This study was designed to determine whether treatment with erythropoietin (EPO) could protect cerebral microvasculature against the pathological consequences of endothelial nitric oxide (NO) synthase uncoupling. Wild-type and GTP cyclohydrolase I (GTPCH-I)-deficient hph1 mice were administered EPO (1000 U/kg/day, s.c., 3 days). Cerebral microvessels of hph1 mice demonstrated reduced tetrahydrobiopterin (BH4) bioavailability, increased production of superoxide anions and impaired endothelial NO signaling. Treatment of hph1 mice with EPO attenuated the levels of 7,8-dihydrobiopterin, the oxidized product of BH4, and significantly increased the ratio of BH4 to 7,8-dihydrobiopterin. Moreover, EPO decreased the levels of superoxide anions and increased NO bioavailability in cerebral microvessels of hph1 mice. Attenuated oxidation of BH4 and inhibition of endothelial NO synthase uncoupling were explained by the increased expression of antioxidant proteins, manganese superoxide dismutase, and catalase. The protective effects of EPO observed in cerebral microvessels of hph1 mice were also observed in GTPCH-I siRNA-treated human brain microvascular endothelial cells exposed to EPO (1 U/mL or 10 U/mL; 3 days). Our results suggest that EPO might protect the neurovascular unit against oxidative stress by restoring bioavailability of BH4 and endothelial NO in the cerebral microvascular endothelium. We demonstrate that treatment with erythropoietin (EPO) could protect cerebral microvasculature against the pathological consequences of endothelial nitric oxide (NO) synthase uncoupling. Our results suggest that EPO might protect the neurovascular unit against oxidative stress by restoring bioavailability of tetrahydrobiopterin (BH4) and endothelial nitric oxide.

Rho kinase: A new target for treatment of cerebral ischemia/reperfusion injury

Rho kinase inhibitor fasudil hydrochloride has been shown to reduce cerebral vasospasm, to inhibit inflammation and apoptosis and to promote the recovery of neurological function. However, the effect of fasudil hydrochloride on claudin-5 protein expression has not been reported after cerebral ischemia/reperfusion. Therefore, this study sought to explore the effects of fasudil hydrochloride on blood-brain barrier permeability, growth-associated protein-43 and claudin-5 protein expression, and to further understand the neuroprotective effect of fasudil hydrochloride. A focal cerebral ischemia/reperfusion model was established using the intraluminal suture technique. Fasudil hydrochloride (15 mg/kg) was intraperitoneally injected once a day. Neurological deficit was evaluated using Longa's method. Changes in permeability of blood-brain barrier were measured using Evans blue. Changes in RhoA, growth-associated protein-43 and claudin-5 protein expression were detected using immunohistochemistry and western blotting. Results revealed that fasudil hydrochloride noticeably contributed to the recovery of neurological function, improved the function of blood-brain barrier, inhibited RhoA protein expression, and upregulated growth-associated protein-43 and claudin-5 protein expression following cerebral ischemia/reperfusion. Results indicated that Rho kinase exhibits a certain effect on neurovascular damage following cerebral ischemia/reperfusion. Intervention targeted Rho kinase might be a new therapeutic target in the treatment of cerebral ischemia/reperfusion.

Linolenic acid provides multi-cellular protective effects after photothrombotic cerebral ischemia in rats

Alpha-linolenic acid (LIN) has been shown to provide neuroprotective effects against cerebral ischemia. LIN is a potent activator of TREK-1 channel and LIN-induced neuroprotection disappears in Trek1-/- mice, suggesting that this channel is directly related to the LIN-induced resistance of brain against ischemia. However, the cellular mechanism underlying LIN induced neuroprotective effects after ischemia remains unclear. In this study, using a rat photochemical brain ischemia model, we investigated the effects of LIN on the protein abundance of astrocytic glutamate transporter and AQP4, microglia activation, cell apoptosis and behavioral recovery following ischemia. Administration of LIN rescued the protein abundance of astrocytic glutamate transporter GLT-1, decreased the protein abundance of AQP4 and brain edema, inhibited microglia activation, attenuated cell apoptosis and improved behavioral function recovery. Meanwhile, TREK-1 was widely distributed in the cortex and hippocampus, primarily localized in astrocytes and neurons. LIN could potentiate the TREK-1 mediated astrocytic passive conductance and hyperpolarize the membrane potential. Our results suggest that LIN provides multiple cellular neuroprotective effects in cerebral ischemia. TREK-1 may serve as a promising multi-mechanism therapeutic target for the treatment of stroke.

HUCBCs increase angiopoietin 1 and induce neurorestorative effects after stroke in T1DM rats

BACKGROUND AND PURPOSE

We investigated the neurorestorative effects and underlying mechanisms of stroke treatment with human umbilical cord blood cells (HUCBCs) in Type one diabetes mellitus (T1DM) rats.

METHODS

Type one diabetes mellitus rats were subjected to middle cerebral artery occlusion (MCAo) and 24 h later were treated with: (1) phosphate-buffered-saline; (2) HUCBCs. Brain endothelial cells (MBECs) were cultured and capillary tube formation was measured.

RESULTS

Human umbilical cord blood cells treatment significantly improved functional outcome and promoted white matter (WM) remodeling, as identified by Bielschowsky silver, Luxol fast blue and SMI-31 expression, increased oligodendrocyte progenitor cell and oligodendrocyte density after stroke in T1DM rats. HUCBC also promoted vascular remodeling, evident from enhanced vascular and arterial density and increased artery diameter, and decreased blood-brain barrier leakage. HUCBC treatment also increased Angiopoietin-1 and decreased receptor for advanced glycation end-products (RAGE) expression compared to T1DM-MCAo control. In vitro analysis of MBECs demonstrated that Ang1 inversely regulated RAGE expression. HUCBC and Ang1 significantly increased capillary tube formation and decreased inflammatory factor expression, while anti-Ang1 attenuated HUCBC-induced tube formation and antiinflammatory effects.

CONCLUSION

Human umbilical cord blood cells is an effective neurorestorative therapy in T1DM-MCAo rats and the enhanced vascular and WM remodeling and associated functional recovery after stroke may be attributed to increasing Angiopoietin-1 and decreasing RAGE.

MRI evaluation of BBB disruption after adjuvant AcSDKP treatment of stroke with tPA in rat

The primary limitation of thrombolytic treatment of ischemic stroke with tissue plasminogen activator (tPA) is the hemorrhagic risk. We tested AcSDKP (N-acetyl-seryl-aspartyl-lysyl-proline), as an auxiliary therapeutic agent, to reduce blood-brain barrier (BBB) disruption in a combination tPA thrombolytic treatment of stroke. Wistar rats subjected to embolic stroke were randomly assigned to either the tPA monotherapy group (n=9) or combination of tPA and AcSDKP treatment group (n=9) initiated at 4 h after ischemia. Magnetic resonance imaging (MRI) measurements were performed before and after the treatments. Immunohistochemical staining and measurements were performed to confirm MRI findings. Longitudinal MRI permeability measurements with gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) demonstrated that combination treatment of acute embolic stroke with AcSDKP and tPA significantly reduced BBB leakage, compared to tPA monotherapy, at 3 and 6 days (18.3±9.8 mm3 vs. 65.0±21.0 mm3, p<0.001) after the onset of stroke, although BBB leakage was comparable between the two groups prior to the treatments (6.8±4.4 mm3 vs. 4.3±3.3 mm3, p>0.18). The substantial reduction of BBB leakage observed in the combination treatment group was closely associated with reduced ischemic lesions measured by T2 maps (113.6±24.9 mm3 vs. 188.1±60.8 mm3, p<0.04 at 6 days). Histopathological analysis of the same population of rats showed that the combination treatment significantly reduced parenchymal fibrin deposition (0.063±0.059 mm2 vs. 0.172±0.103 mm2, p<0.03) and infarct volume (146.7±35.9 mm3 vs. 199.3±60.4 mm3, p<0.05) compared to the tPA monotherapy at 6days after stroke. MRI provides biological insight into the therapeutic benefit of combination treatment of stroke with tPA and AcSDKP 4h after onset, and demonstrates significantly improved cerebrovascular integrity with neuroprotective effects compared with tPA monotherapy.

Combination treatment with N-acetyl-seryl-aspartyl-lysyl-proline and tissue plasminogen activator provides potent neuroprotection in rats after stroke

BACKGROUND AND PURPOSE

N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), an endogenously produced circulating peptide in humans and rodents, exerts anti-inflammatory and cardioprotective activities in various cardiovascular diseases.

METHODS

The present study evaluated the neuroprotective effect of AcSDKP alone and in combination with thrombolytic therapy in a rat model of embolic focal cerebral ischemia.

RESULTS

We found that treatment with AcSDKP alone at 1 hour or the combination treatment with AcSDKP and tissue plasminogen activator (tPA) at 4 hours after stroke onset substantially increased AcSDKP levels in plasma and cerebrospinal fluid and robustly reduced infarct volume and neurological deficits, without increasing the incidence of brain hemorrhage compared with ischemic rats treated with saline, AcSDKP alone at 4 hours, and tPA alone at 4 hours. Moreover, the combination treatment considerably reduced the density of nuclear transcription factor-κB (NF-κB), transforming growth factor β (TGF-β), and plasminogen activator inhibitor-1 (PAI-1) positive cerebral blood vessels in the ischemic brain, all of which were associated with reduced microvascular fibrin extravasation and platelet accumulation compared with tPA monotherapy. In vitro, AcSDKP blocked fibrin-elevated TGF-β1, PAI-1, and NF-κB proteins in primary human brain microvascular endothelial cells.

CONCLUSIONS

Our data indicate that AcSDKP passes the blood-brain barrier, and that treatment of acute stroke with AcSDKP either alone at 1 hour or in combination with tPA at 4 hours of the onset of stroke is effective to reduce ischemic cell damage in a rat model of embolic stroke. Inactivation of TGF-β and NF-κB signaling by AcSDKP in the neurovascular unit may underlie the neuroprotective effect of AcSDKP.

Proton-sensitive cation channels and ion exchangers in ischemic brain injury: new therapeutic targets for stroke?

Ischemic brain injury results from complicated cellular mechanisms. The present therapy for acute ischemic stroke is limited to thrombolysis with the recombinant tissue plasminogen activator (rtPA) and mechanical recanalization. Therefore, a better understanding of ischemic brain injury is needed for the development of more effective therapies. Disruption of ionic homeostasis plays an important role in cell death following cerebral ischemia. Glutamate receptor-mediated ionic imbalance and neurotoxicity have been well established in cerebral ischemia after stroke. However, non-NMDA receptor-dependent mechanisms, involving acid-sensing ion channel 1a (ASIC1a), transient receptor potential melastatin 7 (TRPM7), and Na(+)/H(+) exchanger isoform 1 (NHE1), have recently emerged as important players in the dysregulation of ionic homeostasis in the CNS under ischemic conditions. These H(+)-sensitive channels and/or exchangers are expressed in the majority of cell types of the neurovascular unit. Sustained activation of these proteins causes excessive influx of cations, such as Ca(2+), Na(+), and Zn(2+), and leads to ischemic reperfusion brain injury. In this review, we summarize recent pre-clinical experimental research findings on how these channels/exchangers are regulated in both in vitro and in vivo models of cerebral ischemia. The blockade or transgenic knockdown of these proteins was shown to be neuroprotective in these ischemia models. Taken together, these non-NMDA receptor-dependent mechanisms may serve as novel therapeutic targets for stroke intervention.

Squalenoyl adenosine nanoparticles provide neuroprotection after stroke and spinal cord injury

There is an urgent need to develop new therapeutic approaches for the treatment of severe neurological trauma, such as stroke and spinal cord injuries. However, many drugs with potential neuropharmacological activity, such as adenosine, are inefficient upon systemic administration because of their fast metabolization and rapid clearance from the bloodstream. Here, we show that conjugation of adenosine to the lipid squalene and the subsequent formation of nanoassemblies allows prolonged circulation of this nucleoside, providing neuroprotection in mouse stroke and rat spinal cord injury models. The animals receiving systemic administration of squalenoyl adenosine nanoassemblies showed a significant improvement of their neurologic deficit score in the case of cerebral ischaemia, and an early motor recovery of the hindlimbs in the case of spinal cord injury. Moreover, in vitro and in vivo studies demonstrated that the nanoassemblies were able to extend adenosine circulation and its interaction with the neurovascular unit. This Article shows, for the first time, that a hydrophilic and rapidly metabolized molecule such as adenosine may become pharmacologically efficient owing to a single conjugation with the lipid squalene.

15-Deoxy-∆12,14-PGJ 2, by activating peroxisome proliferator-activated receptor-gamma, suppresses p22phox transcription to protect brain endothelial cells against hypoxia-induced apoptosis

15-Deoxy-∆(12,14)-PGJ(2) (15d-PGJ(2)) and thiazolidinedione attenuate reactive oxygen species (ROS) production via a peroxisome proliferator-activated receptor-gamma (PPAR-γ)-dependent pathway. Nonetheless, how PPAR-γ mediates ROS production to ameliorate ischemic brain injury is not clear. Recent studies indicated that nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is the major source of ROS in the vascular system. In the present study, we used an in vitro oxygen-glucose deprivation and reoxygenation (hypoxia reoxygenation [HR]) paradigm to study whether PPAR-γ interacts with NADPH oxidase, thereby regulating ROS formation in cerebral endothelial cells (CECs). With pharmacological (PPAR-γ antagonist GW9662), loss-of-function (PPAR-γ siRNA), and gain-of-function (Ad-PPAR-γ) approaches, we first demonstrated that 15d-PGJ(2) protected HR-treated CECs against ROS-induced apoptosis in a PPAR-γ-dependent manner. Results of promoter and subcellular localization analyses further revealed that 15d-PGJ(2), by activating PPAR-γ, blocked HR-induced NF-κB nuclear translocation, which led to inhibited transcription of the NADPH oxidase subunit p22phox. In summary, we report a novel transrepression mechanism whereby PPAR-γ downregulates hypoxia-activated p22phox transcription and the subsequent NADPH oxidase activation, ROS formation, and CEC apoptosis.

Nicorandil inhibits inflammasome activation and Toll-like receptor-4 signal transduction to protect against oxygen-glucose deprivation-induced inflammation in BV-2 cells

BACKGROUND AND PURPOSE

Our previous studies have demonstrated adenosine triphosphate-sensitive potassium channel (KATP channel) openers could protect against inflammatory response in brain disease, but little is known about the mechanisms involved in KATP channel openers inhibiting neuroinflammation.

METHODS AND RESULTS

In the present study, we found that oxygen-glucose deprivation (OGD) resulted in BV-2 cells activation, significantly increased tumor necrosis factor-alpha and interleukin-1beta (IL-1β) levels, accompanied by downregulating Kir6.1 subunit. Pretreatment with nicorandil, a KATP channel opener, could attenuate OGD-induced BV-2 cells activation and inhibit pro-inflammatory factors release. Further study demonstrated that OGD activated Toll-like receptor-4 (TLR4) signaling pathway and NOD-like receptor pyrin domain containing three inflammasome, thereby increased IL-1β production. Pretreatment with nicorandil could reverse the two pathways involved in IL-1β production.

CONCLUSIONS

Our findings reveal that KATP channel openers could protect against OGD-induced neuroinflammation via inhibiting inflammasome activation and TLR4 signal transduction.

Effects of pretreatment with a combination of melatonin and electroacupuncture in a rat model of transient focal cerebral ischemia

Both melatonin and electroacupuncture (EA) have been suggested to be effective treatments against stroke. However, it is unknown whether a combination of these two therapies could be beneficial against transient focal cerebral ischemia. The present study investigated the effects of pretreatment of a combination of melatonin and EA in a rat model of transient middle cerebral artery occlusion (MCAO). After pretreatment of melatonin plus EA (MEA), transient MCAO was induced for 90 minutes in male Sprague-Dawley (SD) rats. The neurological deficit score, brain infarct volume, cerebral edema ratio, neuronal inflammation, and apoptosis were evaluated 24 hours after transient MCAO. The expression of related inflammatory and apoptotic mediators in the brain was also investigated. The results showed that MEA improved neurological outcome, reduced brain infarct volume, and inhibited neuronal inflammation as well as apoptosis 24 hours after transient MCAO. The beneficial effects may derive from downregulation of proinflammatory and proapoptotic mediators and upregulation of antiapoptotic mediators. Thus, these results suggest a preventive effect of pretreatment of MEA on transient focal cerebral ischemia.

Preferential lentiviral targeting of astrocytes in the central nervous system

The ability to visualize and genetically manipulate specific cell populations of the central nervous system (CNS) is fundamental to a better understanding of brain functions at the cellular and molecular levels. Tools to selectively target cells of the CNS include molecular genetics, imaging, and use of transgenic animals. However, these approaches are technically challenging, time consuming, and difficult to control. Viral-mediated targeting of cells in the CNS can be highly beneficial for studying and treating neurodegenerative diseases. Yet, despite specific marking of numerous cell types in the CNS, in vivo selective targeting of astrocytes has not been optimized. In this study, preferential targeting of astrocytes in the CNS was demonstrated using engineered lentiviruses that were pseudotyped with a modified Sindbis envelope and displayed anti-GLAST IgG on their surfaces as an attachment moiety. Viral tropism for astrocytes was initially verified in vitro in primary mixed glia cultures. When injected into the brains of mice, lentiviruses that displayed GLAST IgG on their surface, exhibited preferential astrocyte targeting, compared to pseudotyped lentiviruses that did not incorporate any IgG or that expressed a control isotype IgG. Overall, this approach is highly flexible and can be exploited to selectively target astrocytes or other cell types of the CNS. As such, it can open a window to visualize and genetically manipulate astrocytes or other cells of the CNS as means of research and treatment.

Combined antiapoptotic and antioxidant approach to acute neuroprotection for stroke in hypertensive rats

We hypothesized that targeting key points in the ischemic cascade with combined neuroglobin (Ngb) overexpression and c-jun N-terminal kinase (JNK) inhibition (SP600125) would offer greater neuroprotection than single treatment after in vitro hypoxia/reoxygenation and in a randomized, blinded in vivo experimental stroke study using a clinically relevant rat strain. Male spontaneously hypertensive stroke-prone rats underwent transient middle cerebral artery occlusion (tMCAO) and were divided into the following groups: tMCAO; tMCAO+control GFP-expressing canine adenovirus-2, CAVGFP; tMCAO+Ngb-expressing CAV-2, CAVNgb; tMCAO+SP600125; tMCAO+CAVNgb+SP600125; or sham procedure. Rats were assessed till day 14 for neurologic outcome before infarct determination. In vitro, combined lentivirus-mediated Ngb overexpression+SP600125 significantly reduced oxidative stress and apoptosis compared with single treatment(s) after hypoxia/reoxygenation in B50 cells. In vivo, infarct volume was significantly reduced by CAVNgb, SP600125, and further by CAVNgb+SP600125. The number of Ngb-positive cells in the peri-infarct cortex and striatum was significantly increased 14 days after tMCAO in animals receiving CAVNgb. Neurologic outcome, measured using a 32-point neurologic score, significantly improved with CAVNgb+SP600125 compared with single treatments at 14 days after tMCAO. Combined Ngb overexpression with JNK inhibition reduced hypoxia/reoxygenation-induced oxidative stress and apoptosis in cultured neurons and reduced infarct and improved neurologic outcome more than single therapy after in vivo experimental stroke in hypertensive rats.

Cell-based therapy for ischemic stroke

INTRODUCTION

Stroke is a major cause of mortality and disability in adults worldwide. Unfortunately, current therapy which targets vessel recanalization has a narrow treatment window, and at this time neuroprotective approaches are not effective for stroke treatment. However, after stroke the parenchymal and endothelial cells in the central nervous system (CNS) respond in concert to ischemic stressors and create a microenvironment in which successful recovery may ensue. Neurogenesis, synaptogenesis, axonal sprouting, glial cell activation, angiogenesis and vascular remodeling within the brain and the spinal cord are stimulated post stroke. Cell based-therapy amplifies these endogenous restorative effects within the CNS to promote functional outcome.

AREAS COVERED

This article reviews current knowledge of cell-based therapy in the adult brain after stroke, including transplanted cell type, benefits and risks, with an emphasis on mechanisms of action.

EXPERT OPINION

Experimental studies and clinical trials with cell-based therapy in stroke appear promising. Cell-based therapy is not intended for the replacement of damaged cells, but for the remodeling of the CNS by promoting neuroplasticity, angiogenesis and immunomodulation. However, there are risks associated with the use of cell-based therapy, and adequate evaluation of these potential risks is a prerequisite before clinical application for stroke patients.

Drug-like property profiling of novel neuroprotective compounds to treat acute ischemic stroke: guidelines to develop pleiotropic molecules

The development of novel neuroprotective compounds to treat acute ischemic stroke (AIS) has been problematic and quite complicated, since many candidates that have been tested clinically lacked significant pleiotropic activity, were unable to effectively cross the blood brain barrier (BBB), had poor bioavailability or were toxic. Moreover, the compounds did not confer significant neuroprotection or clinical efficacy measured using standard behavioral endpoints, when studied in clinical trials in a heterogeneous population of stroke patients. To circumvent some of the drug development problems describe above, we have used a rational funnel approach to identify and develop promising candidates. Using a step-wise approach, we have identified a series of compounds based upon two different neuroprotection assays. We have then taken the candidates and determined their "drug-like" properties. This guidelines article details in vitro screening assays used to show pleiotropic activity of a series of novel compounds; including enhanced neuroprotective activity compared to the parent compound fisetin. Moreover, for preliminary drug de-risking or risk reduction during development, we used compound assessment in the CeeTox assay, ADME toxicity using the AMES test for genotoxicity and interaction with Cytochrome P450 using CYP450 inhibition analysis against a spectrum of CYP450 enzymes (CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4) as a measure of drug interaction. Moreover, the compounds have been studied using a transfected Madin Darby canine kidney (MDCK) cell assay to assess blood brain barrier penetration (BBB). Using this series of assays, we have identified 4 novel molecules to be developed as an AIS treatment.

Kir6.1 knockdown aggravates cerebral ischemia/reperfusion-induced neural injury in mice

BACKGROUND AND PURPOSE

ATP-sensitive potassium (K-ATP) channels couple energy metabolism with electric activity, which play important roles in brain diseases including stroke. However, the impacts of Kir6.1-containing K-ATP channels that mainly expressed on glia in stroke remain unclear.

METHODS AND RESULTS

In this study, we found that expression of Kir6.1 was significantly decreased in the ischemic brain area of C57BL/6J mice after 1-h middle cerebral artery occlusion (MCAO) and 24-h reperfusion. Then, we subjected Kir6.1 heterozygote knockout (Kir6.1(+/-) ) mice to cerebral ischemia/reperfusion (I/R) injury and found that Kir6.1(+/-) mice exhibited exacerbated neurological disorder and enlarged infarct size, companied by glial over-activation and blood-brain barrier (BBB) damages. Furthermore, we showed that Kir6.1 knockdown aggravated endoplasmic reticulum (ER) stress and thereby increased the levels of proinflammatory factors tumor necrosis factor-α and interleukin-1β (TNF-α and IL-1β) in mouse brain.

CONCLUSIONS

Our findings reveal that Kir6.1 knockdown exacerbates cerebral I/R-induced brain damages via increasing ER stress and inflammatory response, indicating that Kir6.1-containing K-ATP channels may be a potential therapeutic target for stroke.

[Experimental therapy approaches for ischemic stroke]

In Germany, as in most other industrialized countries, ischemic stroke is the leading cause of disability and the third leading cause of death. As the incidence of ischemic stroke increases with age it is expected that this problem will become even more urgent in an aging society. Despite significant research efforts on the clinical as well as on the experimental level, treatment of ischemic stroke is still based on general intensive care measures and on reperfusion therapy with recombinant tissue plasminogen activator (rtPA); however, rtPA is not suitable for a wide range of patients and is restricted to a therapeutic window of 4.5 h due to an increasing risk of bleeding. Accordingly, novel therapeutic options for ischemic stroke are urgently need. The current review discusses novel experimental therapeutic principles for ischemic stroke which may have clinical potential. The main topics are neuroprotection and strategies addressing the immune system.